The Internet has dramatically increased the potential for data, voice, and video services for customers. Existing circuit-switched telephony systems, however, do not provide the foundation to support the growing need for bandwidth and new services required by both residential and business consumers. As a result, integrated access devices have been introduced to support Internet and related technologies as well as standard telephony service for consumers.
Integrated access devices often combine synchronous and asynchronous transport and switch functionality to multiplex data, voice, and video traffic together onto a single network. Within an integrated access device, a time division multiplex (TDM) bus is typically used to transport voice and other synchronous traffic between the line cards and a switch core. An asynchronous transfer mode (ATM) bus is used to transport ATM traffic between the line cards and the switch core. At the switch core, traffic may be converted between TDM and ATM formats for high speed transmission on the network and for distribution to customer premises.
The TDM bus carries voice traffic from the various telephony interfaces, such as plain old telephone service (POTS), T1, and DS3, to the switch core. The TDM bus typically has a frame structure that repeats on 125 microsecond intervals, in accordance with the frame periods of the telephony interfaces. Traditionally, TDM buses have been very simplistic in their operation. While this limits their functionality, it optimizes bandwidth utilization over the backplane of the device.